Oil or tar sands are black sand formations chiefly dating from the Mesozoic, which are spread worldwide and have a mineral oil content of about 5 to 18%. In contrast to liquid petroleum, the oil sands are thickly viscous and must first be separated from the sand and be processed to crude oil. In the regions near the surface, the oil sand is recovered by strip mining by means of huge bucket-wheel and dragline excavators and ground to a grain size <30 μm. The heavy oil is extracted by means of hot water and steam, wherein at the top a suspension with organic phase is accumulated. The lower part is separated and repurified. Therefore, much water is required for oil recovery, which in addition is discharged not quite oil-free.
Oil shale refers to mountain-forming formations of marl or other types of clayey bituminous sediment rock from various geological eras, which are rich in organic matter (kerogen) from fossilized microorganisms or from pollen. The recovery of oil from oil shale traditionally is effected by mining and subsequent pyrolysis (carbonization at 500° C.). Alternatively, underground recovery (in situ) is used by injecting a steam-air mixture into the rock, which was previously loosened by blasting, and igniting a flame front which expels the oil.
The recovery of crude oil from oil sands or oil shale is thus relatively cost-intensive. With rising petroleum prices, the recovery of crude oil from oil sands and oil shale, however, becomes increasingly interesting in economic terms. A problem in the present recovery of oil from oil sands and tar sands is the necessary high consumption of water and the emission of waste waters containing residual oil.
U.S. Pat. No. 4,507,195 describes a process for coking contaminated oil shale or tar sand oil on solids distilled in retorts. The hydrocarbonaceous solids are mixed with a hot heat-transfer material in order to raise the temperature of the solids to a temperature suitable for the pyrolysis of the hydrocarbons. The mixture is kept in the pyrolysis zone, until a sufficient quantity of hydrocarbon vapors is released. In the pyrolysis zone a stripping gas is passed through the mixture in order to lower the dew point of the evolved hydrocarbon vapors and to entrain the fine particles. Accordingly, a mixture of contaminated hydrocarbon vapors, stripping gas and entrained fine particles is obtained from the pyrolysis zone. From the contaminated hydrocarbon vapors, a heavy fraction is separated and thermally cracked in a fluidized bed consisting of the fine particles, whereby the impurities along with the coke are deposited on the fine particles in the fluidized bed. The product oil vapors are withdrawn from the coking tank. As heat-transfer material, recirculated pyrolyzed oil shale or tar sand is used, which has been passed through a combustion zone, in order to burn off carbon residues and provide the heat for the pyrolysis of the raw material. Since there is no pressure seal between the combustion zone and the pyrolysis furnace, the oxidizing atmosphere of the combustion zone can enter the pyrolysis furnace and impair the quality of the oil vapor. In addition, thermal cracking in the coking tank consumes much energy and therefore is expensive.
EP 1 015 527 B1 describes a process for the thermal treatment of feedstock containing volatile, combustible constituents, wherein the feedstock is mixed with hot granular solids from a collecting bin in a pyrolysis reactor in which relatively high temperatures exist. In the reactor, cracking reactions in the gases and vapors should be caused thereby.
Beside the thermal cracking used in the above-mentioned processes, catalytic cracking processes are also known. In Fluid Catalytic Cracking (FCC), the heavy distillate of a refinery is broken down into gases, liquefied gases and gasolines, preferably into long-chain n-alkanes and i-alkanes. Cracking generally is effected at temperatures between 450 and 550° C. and a reactor pressure of 1.4 bar by means of an alumosilicate-based zeolite catalyst. FCC crackers are described, for example, in U.S. Pat. No. 7,135,151 B1, US 2005/0118076 A1 and US 2006/0231459 A1. An exemplary catalyst is disclosed in WO 2006/131506 A1.